1 /* (C) 1999-2001 Paul `Rusty' Russell
2 * (C) 2002-2006 Netfilter Core Team <coreteam@netfilter.org>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License version 2 as
6 * published by the Free Software Foundation.
7 */
8
9 #include <linux/types.h>
10 #include <linux/init.h>
11 #include <linux/export.h>
12 #include <linux/tcp.h>
13
14 #include <linux/netfilter.h>
15 #include <linux/netfilter/nfnetlink_conntrack.h>
16 #include <net/netfilter/nf_nat.h>
17 #include <net/netfilter/nf_nat_l3proto.h>
18 #include <net/netfilter/nf_nat_l4proto.h>
19 #include <net/netfilter/nf_nat_core.h>
20
21 static u16 tcp_port_rover;
22
23 static void
tcp_unique_tuple(const struct nf_nat_l3proto * l3proto,struct nf_conntrack_tuple * tuple,const struct nf_nat_range * range,enum nf_nat_manip_type maniptype,const struct nf_conn * ct)24 tcp_unique_tuple(const struct nf_nat_l3proto *l3proto,
25 struct nf_conntrack_tuple *tuple,
26 const struct nf_nat_range *range,
27 enum nf_nat_manip_type maniptype,
28 const struct nf_conn *ct)
29 {
30 nf_nat_l4proto_unique_tuple(l3proto, tuple, range, maniptype, ct,
31 &tcp_port_rover);
32 }
33
34 static bool
tcp_manip_pkt(struct sk_buff * skb,const struct nf_nat_l3proto * l3proto,unsigned int iphdroff,unsigned int hdroff,const struct nf_conntrack_tuple * tuple,enum nf_nat_manip_type maniptype)35 tcp_manip_pkt(struct sk_buff *skb,
36 const struct nf_nat_l3proto *l3proto,
37 unsigned int iphdroff, unsigned int hdroff,
38 const struct nf_conntrack_tuple *tuple,
39 enum nf_nat_manip_type maniptype)
40 {
41 struct tcphdr *hdr;
42 __be16 *portptr, newport, oldport;
43 int hdrsize = 8; /* TCP connection tracking guarantees this much */
44
45 /* this could be a inner header returned in icmp packet; in such
46 cases we cannot update the checksum field since it is outside of
47 the 8 bytes of transport layer headers we are guaranteed */
48 if (skb->len >= hdroff + sizeof(struct tcphdr))
49 hdrsize = sizeof(struct tcphdr);
50
51 if (!skb_make_writable(skb, hdroff + hdrsize))
52 return false;
53
54 hdr = (struct tcphdr *)(skb->data + hdroff);
55
56 if (maniptype == NF_NAT_MANIP_SRC) {
57 /* Get rid of src port */
58 newport = tuple->src.u.tcp.port;
59 portptr = &hdr->source;
60 } else {
61 /* Get rid of dst port */
62 newport = tuple->dst.u.tcp.port;
63 portptr = &hdr->dest;
64 }
65
66 oldport = *portptr;
67 *portptr = newport;
68
69 if (hdrsize < sizeof(*hdr))
70 return true;
71
72 l3proto->csum_update(skb, iphdroff, &hdr->check, tuple, maniptype);
73 inet_proto_csum_replace2(&hdr->check, skb, oldport, newport, false);
74 return true;
75 }
76
77 const struct nf_nat_l4proto nf_nat_l4proto_tcp = {
78 .l4proto = IPPROTO_TCP,
79 .manip_pkt = tcp_manip_pkt,
80 .in_range = nf_nat_l4proto_in_range,
81 .unique_tuple = tcp_unique_tuple,
82 #if IS_ENABLED(CONFIG_NF_CT_NETLINK)
83 .nlattr_to_range = nf_nat_l4proto_nlattr_to_range,
84 #endif
85 };
86